Coupled range finder



Jan. 28, 1941. O LlEBMANN 2,229,855

COUPLED RANGE FINDER Original Filed Feb. 18, 1939 06cm- Lfebmann 28 11v VENTOYR .A TTORNE Y focusing mechanism Patented Jan. 28, 1941 UNITED STATES PATENT OFFICE COUPLED RANGE FINDER Oscar Liebmann, Bergenfiel-d, N. J., assignor to Q. 0. S. Corporation, poration of New York New York, N. Y., a. cor- 1 Claim.

This is a division of my copending application, Serial No. 257,038, filed February 18, 1939, and relates to improvements in range finders of the type used with motion picture cameras and which are coupled mechanically to the focusing mechanism whereby correct focusing is obtainable at any distance, and in particular, the invention relates to the mechanical coupling means linking the range finder with the lens mechanism.

An important object of my invention is to provide a type of coupling which will give the utmost precision in the adjustments of the focus.

A further object of my invention is to provide a range finder which can be manufactured in quantities at low cost and mounted on cameras with various types of lenses with only minor adjustments, and without making special cams or other devices for each individual camera. Other objects and advantages of my invention will be apparent during the course of the following description.

In the accompanying drawing, forming a part of this specification, and in which like numerals are employed to designate like parts throughout the same-- Figure 1 is a plan view of a motion picture camera equipped with a preferred embodiment of my invention,

Figure 2 is a side elevation of the same camera and range finder,

Figure 3 is a detail plan view of the rotatable reflector mechanism of the range finder, and,

Figure 4 is a schematic diagram of the range finder.

Referring to the drawing, the numeral I0 designates an ordinary amateur type, motion picture camera with lens H. On the rotatable lens is rigidly mounted the knurled sleeve l2 the rear face of which is partly milled away to form a special curve, similar to that of the thread of a screw, beginning at the point designated D and ending at E, see Figure l. A bracket I3 is mounted rigidly on the side of the camera I0 and a rod I4 is slidable longitudinally in the holes formed in the ends of the bracket l3. A coil spring I5 is placed around the rod l4 and is fastened to I4 at one end by the screw I6. the other end being fastened to bracket I3. A rigid rod I1 is fastened securely to rod I4 and is extending in an are over to the rotatable sleeve l2 where the end of rod i1 is pushed up against the curved face of sleeve I2 by the action of spring l5. The rear end of rod 14 carries a centrally located adjusting screw Hi from which a pin l9 extends into the range finder housing 20. This housing 20 is usually made up from a square tubing closed at both ends. It contains a range finder of the usual type with one semitransparent reflector with lens 2| and eye piece 22 and one rotatable reflector with lens 23, see Figure 1. The range finder housing 20 is mounted transversely across the camera on a bracket 24 (Fig. 2) in a manner such that lenses 2| and 23 are afforded an unobstructed view forward.

In Figure 3 is shown in detail the interior mechanism of the range finder. The rotatable reflector 25 is pivoted at 26 and is mounted on the triangular block 21 which has milled slots 28 to prevent warping. The block 21 is fastened to a lever 29 which is held against pin l9 by spring 30. The spring 30 is twisted around screw 3| and the end is fastened in hole 32.

The operation of my invention is based upon the well known principle of the range finder as illustrated in Figure 4. The semi-transparent reflector is located at O and the rotatable reflector 25 is located at B, the distance b between OB is fixed and if an object is located at X the distance OX=a=b tan A, where A is the angle between OB and BX.

Referring now to Figures 1, 2 and 3, it is obvious upon inspection that when the knurled sleeve I2 is turned the end of the rod I! will follow the curved cam surface from E to D, and in so doing the rod I! will transfer its longitudinal motion to the rod I which will again transfer the motion through the pin l9 to the lever 29 and thereby giving the reflector 25 a slight rotational movement. While turning sleeve l2 the operator looks through window 22 until coincidence is obtained, and the coupling mechanism is precalibrated in such a way that when the range finder shows coincidence the lens is focused to the correct distance. It was previously through that it would be sufficient that the cam surface from D to E would described a straight line, but it was found that this resulted in very considerable inaccuracies on distances near the ends of the range. A curve may be found by calculation, but a more satisfactory way is to determine the same by exact experimental methods. It has been found that by so doing it is possible to make use of the same curve for lenses of various types merely by making slight adjustments of the screw [8.

It is to be understood that the form of my invention, herewith shown and described, is to be taken as a preferred example of same, and that spring loaded and slidably mounted parallel to the axis of the camera and on the outside of same; a double ended adjustable thumb screw adjustably fastened to the rear end of said cylindrical rod, one end of said thumb screw being in operable engagement with said lever and said rotatable mirror; a curved cam fastened to the rotatable part of the lense focusing mechanism of the camera, and a curved rod fastened with one end to said cylindrical rod and suitably bent so as to engage said rotatable curved cam to the lens focusing mechanism with its other end.

OSCAR LIEBMANN. 

